Predator avoidance and dietary fibre predict diurnality in the cathemeral folivore Hapalemur meridionalis

Cathemerality: a key temporal niche

Given the marked variation in abiotic and biotic conditions between day and night, many species specialise their physical activity to being diurnal or nocturnal, and it was long thought that these strategies were commonly fairly fixed and invariant. The term 'cathemeral', was coined in 1987, when Tattersall noted activity in a Madagascan primate during the hours of both daylight and darkness. Initially thought to be rare, cathemerality is now known to be a quite widespread form of time partitioning amongst arthropods, fish, birds, and mammals. Herein we provide a synthesis of present understanding of cathemeral behaviour, arguing that it should routinely be included alongside diurnal and nocturnal strategies in schemes that distinguish and categorise species across taxa according to temporal niche. This synthesis is particularly timely because (i) the study of animal activity patterns is being revolutionised by new and improved technologies; (ii) it is becoming apparent that cathemerality covers a diverse range of obligate to facultative forms, each with their own common sets of functional traits, geographic ranges and evolutionary history; (iii) daytime and nighttime activity likely plays an important but currently neglected role in temporal niche partitioning and ecosystem functioning; and (iv) cathemerality may have an important role in the ability of species to adapt to human-mediated pressures.

Temperature and exudativory as drivers of the marmoset (Callithrix spp.) daily activity period

Primates are affected by fluctuations in ambient temperatures, mostly through thermoregulatory costs and changes in the availability of food. In the present study, we investigate whether the ambient temperature and proxies of food availability affect the activity period of marmosets (Callithrix spp.). We predicted that: (i) at colder sites, marmosets would spend more time at sleeping sites; (ii) midday resting bouts would be longer at hotter sites; (iii) the onset/cessation of activity and resting behavior at midday would be more closely related to temperature than food availability, and (iv) highly exudativorous groups would have higher total levels of resting. We compiled data on the onset and cessation of activity and the time spent resting at midday from seven marmoset studies from sites with a wide range of temperatures. We used generalized linear mixed models to verify the relationship between the dependent variables (lag between dawn and the onset of activities, lag between cessation of activities and dusk, and proportion of resting during midday) and the minimum and maximum temperatures at the respective study sites, together with proxies of food availability (exudativory rates, the amount of habitat available per individual, and net primary productivity) using each sample month as a sampling unit and the identity of the study as a categorical random factor. At colder sites and during colder months, the marmosets left sleeping trees later in the morning and ceased their activities earlier, while at hotter sites and during hotter months, they spent more time resting during midday. More exudativorous groups become active later in the morning, but also ceased their activities later. The abundance of food did not affect the timing of activities. We provide evidence that both low and high temperatures affect marmosets' activities, and that their activity period appears to be more influenced by the thermal environment than food availability.

Seasonal variability in the diet and feeding ecology of black-and-white ruffed lemurs (Varecia variegata) in Ranomafana National Park, southeastern Madagascar

OBJECTIVES

We characterized the diet and foraging ecology of the black-and-white ruffed lemur (Varecia variegata), a specialized frugivore, and investigated behavioral strategies exhibited in response to seasonal changes in resource availability.

MATERIALS AND METHODS

Behavioral data were collected from the same two adjacent communities across 29 months during two observation periods (2007-2008; 2017-2018) in Mangevo, a primary rainforest habitat in southeastern Madagascar. To analyze feeding in the context of energy maximization versus time minimization strategies, we used nonparametric tests to compare plant part constituents, dietary diversity, activity budgets, and canopy strata use between fruit-abundant versus fruit-lean seasons.

RESULTS

Individuals dedicated ~30% of their time to feeding year-round, mostly in the middle canopy (11-20 m). Animals fed primarily on fruits (74% of diet), but frugivory decreased and folivory increased markedly during fruit-lean seasons. Abundant season dietary diversity (98 taxa, H' = 0.71-1.37) was greater than lean season diversity (70 taxa, H' = 0.56-1.06), which coincided with less traveling, more resting, and higher canopy use-though interannual variation was observed.

CONCLUSIONS

Herein, we describe behavioral and dietary patterns that are concordant with a time minimizing behavioral strategy. Black-and-white ruffed lemur diets comprised lower taxonomic diversity, fewer fruits, and more leaves during fruit-lean months. Further, shifts toward less travel, more resting, and greater use of higher canopy levels during this time were most likely for thermoregulatory benefits.

Circadian activity of the swamp rat (Rattus lutreolus) in South Central Victoria

The swamp rat (Rattus lutreolus) is one of the few Australian terrestrial mammals that is commonly active between dawn and dusk. The species has typically been considered cathemeral (active throughout the diel cycle) with variation in circadian activity dependant on proximate factors such as the risk of predation or competition with closely related taxa. Data from camera trapping over 8 years and across 79 sites in South Central Victoria confirmed the species was effectively diurnal throughout the region and that night activity was relatively uncommon. Activity generally tracked daily temperature cycles; lowest in the period prior to dawn and highest in the middle of the afternoon and is consistent with an energy conservation strategy linked to the species’ unusual diet. Other rodent taxa, including two widespread exotic species were strictly nocturnal yet there was little evidence to suggest that R. lutreolus activity was influenced by the presence or absence of other murids or the risk of predation.